3. According to the U.S. Census Bureau, the expectation of life at birth (in years) in the year 2001 for selected nations was as follows: Table 3. Argentina Australia Belgium Brazil Canada Chile China Egypt France Germany Greece 75.3 79.9 78,0 63.2 79.6 75.9 71.6 63.7 78.9 India Indonesia Italy Japan Mexico Netherlands 77.6 78.6 Russia Spain Ukraine 66.1 69,4 80.2 81.7 74.1 79.8 68.8 80.2 66.2 77.8 77.3 United Kingdom United States a) Find the mean expectation of life at birth for these selected nations. b) Explain (do not solve) how part (a) would change if the years were weighted by the size of the human population these nations.